Producing ammonia



March 15, 1932. o. PYZEL PRODUCING AMMONIA Filed Sept. 26. 1928 P k w w 0 C Comp/255w u Hea/ fxc/mnger fxpans/bn 0e wbe Amman/'0 fieponafor [N VEN TOR Jan/'e/ Pyze/ Affomgy Patented Mar. 15,1932

- UNITED STATES PATENT. OFFICE;

DANIEL PYZEL, or PIEDMONT, cALIronNIA, AssIGN n To SHELL DEVELOP ENT com- PANY, OF SAN FRANCISCO, CALIFORNIA, a CORPORATION OF. DELAWARE 1 PRODUCINGIVAMMVCIJNIA Application filed Se tembe 2e,'192s. Serial No. 308,511.

This invention relates tothe production'of ammonia by the catalytic conversion of a mixtureof nitrogen and hydrogen. I v

It is an object of this inventionto ro. vide a process whereby the operating conditions for the catalytic converter andthe ammonia separating elements can be variedindependently.

.lytic converter.

F urther objects and advantages will appear from the following description ofmy invention. y 1

In the production ofammonia by catalytic treatment of a mixture of hydrogen and niconverter, to a temperature at which the ain monia can be easily separated by l1quefac-1 tion or absorption;

Uniform pressure 18 thus maintalned on all I the elements of the plant, only such differences of pressure being caused to exist as will be required to overcome the frictlonal res stance encountered by the circulating gases in the apparatus.

:The ammonia is thus liquefied or absorbed at substantially the same pressure as is ma1ntained .on the catalytic converter. Since the pressures used by the various processes are 7 very high, ranging from 200 atmospheres to as high as 1000 atmospheres, efiicient removal of ammonia has given very little dilficultya Recently more efficient catalysts have been discovered, which allow a decrease in the pressure required on the catalytic, converter, one catalyst giving economical conversion at pressures as low as sixty atmospheres.

While these lower pressures Offer many advantages in the way of simplified construction of catalytic converter apparatus, they introduce considerable difficulties at the ammonia separating elements of the plant.

Now I have found that these difiiculties can be eliminated and yet'the advantages of low pressure conversion retained by the use of the process hereinafter described. e I

Essentially the process em i thefol lowing steps: contacting a hydrogen and nitrogen mixture at a certain pressure and temperature with a catalytic agent; decreasing the temperature-of the converted gas toa temperature suitable for the compression of the gas; compressing'the gas to a'h'igher pressure sufficient for theefiicient removal of the ammonia'contained'in thegas; further' decreasing the temperature of the compres'sed gas'to a temperature at which the ammonia is liquefied or can be absorbed {separating the liquid ammonia or the enriched absorbent from the hydrogen and nitrogen'gas "and exfurther catalytic treatment. l

The process is illustrated in-a simplified way in the accompanying diagram.

panding the remaining hydrogen and nitro- 7 gen gas mlxtureto a pressure suitable for The nitrogen hydrogen mixture at afsuitable pressure, for instance atmza'passes through conduit 1, through heat. exchanger 2 and'through conduit 3 into'the catalytic COIIVGICQIAL, where a fraction of the gases is converted into ammonia. The rich gas flows from the converter through conduit 5, is then cooled in the'heat exchanger 2 to a temperature suitable for the compression of the gas. The cool gas flowsthrough conduit 6, into the compressor 7 where the gas is compressed to the pressure required by the ammonia separator, for instance 140 to 200 atmospheres. The compressed gas is then again'subjected to cooling in the heat exchanger 9 connected to the compressor by conduit 8. The'gas issuing from heat exchanger 9 passes through 'conduit lO into the ammonia separator 11,

Where the liquid ammonia, condensed due to the combined effect of the low temperature producedinthe heat'exchanger 9,'and the high pressure maintained on the gas, is separated from the hydrogen and nitrogen gas mixture. The liquefied ammonia is removed through the conduit 12 controlled by the valve 13. l

The hydrogen and nitrogen gas mixtu're remaining after separationof the ammonia leaves the separator llthrough'conduit 14 and the expansion valve or other expansion device at 15. Here the pressure of the gas is allowed to decrease to such a value as is required by the subsequent treatment of this gas. For instance the gas can be returned for further catalytic treatment to the converter, as its pressure after expansion can be adjusted to the pressure required or this purpose-1n that case he expanded'gas passes directly from the heat exchanger 9 7 through conduit 16 and valve 23 into the conduit 1 and thence on to the converter. Or part or all of the gas may be removed "from the systemthrough conduit 19 and valve 20, and if so desired again subjected to a similar treatment. y

"Fresh hydrogen and nitrogen mixture is obtained under pressure from' some source, not shown, through conduit 22 controlled by valve 21, or if desired this gas can beadded at. some other stage of the process, for instance, through conduit 17 and valve 18.

The expansion of the stripped gasesissuing from the ammonia separator is carrier out, either by the use of an expansion valve or by expansion under the performance of external work, and in such a manner that full use is made of the cooling effect obtainable from this expansion for the purpose of cooling therich gas on its way to the ammonia separator.

I, While, a diagrammatic representation of this process is shown on the attached drawing, it should beunderstood that other arrangements oflheat exchangers and other e. units may be found suitable to carry out the v-method and obtaln the results of thisinvention, and I do not intend to limit myself to ,theparticulararrangement shown; it should furtherbe understood that the arrangement shown is purposely simplified.

In actual operationadditional heating and cooling means must be provided. These may be located, for instance, in lieu oi? the conduits 1,. 3, 5, 6, Sand 1.0. The particular 7 number and arrangement of these devices is not pertinent to the process of this invention taining the increased pressure, expanding the mlxture to the lower pressure prevailing during the conversion, passing the mixture again over the catalyst, and adding'fresh mixture to maintain constant conditions of pressure inthe cycle. I

2; A process of producing ammonia by the catalytic conversion of a mixture of nitrogen and hydrogen, comprising: passing the mixture under pressure over a catalyst, subjectingthe partly converted mixture of gases to a pressure substantially higher than and independent of the pressure maintained during the conversion, cooling the mixture by heat exchange with the gases from which the ammonia has been.removed,'and removing from the mixture the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower pressure prevailing during, the conversion, passing the mixture again over the catalyst, and adding freshmixture to maintain constantconditions of pressure in the cycle. A

8. Aprocess of producing ammoniaby the catalytic conversion of a mixture of nitrogen and hydrogen, comprising: passing the mixture under pressure over a catalyst, subject-- ing the partly converted mlxture oi gasesto a pressure substantially. hlgher than and iny de a'endent or the pressure maintained during the conversion, cooling the mixture by heat exchange with the gases, from which the ammoniahas been removed, immediately'after their expansion, and removing from the mixture the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower pressure prevailing during the conversion, passing the mixture again over the catalyst and adding fresh mixture to maintain constant conditions of pressure in the cycle. I

' 4:. A process of producing ammonia by the catalytic conversion of a mixture of nitrogen and hydrogen, comprising: passing the mixture under pressure over a catalyst, subjecting the partly converted mixture of gases to a pressure substantially higher than and independent of the pressure maintained during the conversion, cooling the mixture and removing the ammonia formed, while maim taining the increased pressure, expanding the mixture to the lower pressure prevailing during the conversion and subjecting the mixture again to a similar treatment in a subsequent stage. r

5. A process of producing ammonia by the catalytic conversion of a mixture of nitrogen and hydrogen, comprising: passing themixture under pressure over a catalyst, subjecting the partly converted mixture of gases to a pressure substantially higher than and independent of the pressure maintained during the conversion, cooling the mixture and removing the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower pressure prevailing during the conversion and subjecting the mixture repeatedly to a similar treatment, in subsequent stages.

6. A process of producing ammonia by the catalytic conversion of a mixture o f'nitrogen I and hydrogen, comprising: passing the mix dependent of the pressure maintained dur-' ing the conversion, cooling the mixture and removing the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower, pressure prevailing during the conversion, passing part of the mixture again over. the catalyst, and subjecting the other part to a similar treatment in a subsequent stage.

7. A process of producing ammonia by the catalytic conversion of a mixtureof nitrogenand hydrogen, comprising: passing the mixture under pressure over a catalyst, s11bj ecting the partly converted mixture of ases to a pressure'substantially higher than and independent of the pressure maintained during the conversion, cooling the mixture by heat exchange without additional external refrigeration and removing from the mixture the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower pressure prevailing during the conversion, passing the mixture again over the catalyst and adding fresh mixture to maintain constant conditions of pressure in the cycle.

8. A process of producing ammonia comprising the steps of compressing a gaseous mixture of nitrogen and hydrogen containing ammonia, cooling the sure, expanding the'residual gas, rom which ammonia has been removed, to a lower pressure, partially converting said residual gas to ammonia by catalysis under this lower pressure and further treating the gaseous mixture again in the manner set out above thereby completing the cycle.

9. A process of producing ammonia as described in claim 8 wherein fresh mixtures 01": hydrogen and nitrogen are continuously added to the expanded residual-gas under a pressure equal to that of the residual gas.

10. A process of producing ammonia by the catalytic conversion of a mixture of nitrogen and hydrogen, comprising: passing the mixture over a catalyst at a relatively low pressure of the order of 50-150 atmospheres, subjecting the part1 converted mixture of gases to an indepen ent pressure at least 50 gen and hydrogen, comprising: prising the mixture over a catalyst at a relatively low pressure of the'order of 100 atm., subjecting the partly converted mixture of gases to an independent pressure of the order of 200 atm.,

cooling the mixture by heat exchange without additional external refrigeration and removing from the mixture the ammonia formed, while maintaining the increased pressure, expanding the mixture to the lower pressure prevaillng during the conversion, passing the mixture again over the catalyst and adding fresh mixture to maintain constant conditions of pressure in the cycle.

, A process of producing ammonia com prlsing the steps of compressing a gaseous mixture of nitrogen and hydrogen containing ammonia to a pressure of the order of 200 atm., cooling the gaseous mixture and removing ammonia under the imposed pressure,

expanding'the residual gas, from which ammon'ia has been removed, to a lower pressure of the order of 100 atm., partially converting said residual gas to ammonia by catalysis under this lower. pressure and further treating the gaseous mixture again in the manner' set out above thereby completing the cycle. M V 1 In testimony whereof, I have hereunto set my hand.

DANIEL PYZEL.

aseous mixture and v removing ammonia un er the lmposedpresatm. higher, cooling the mixture by heat exchange without additional external refrigeration and removing from the mixture the ammonia formed, while maintaining the increased pressure, expanding the mixture to' iao 

